The HTC HD2 is probably one of the most enduring mobile phones out there. While it originally shipped with Windows Mobile way back in 2009, it has become one of the most hacker-friendly devices out there, and hackers have managed to port virtually everything to the device - various versions of Android, MeeGo, Ubuntu, and Windows Phone have found their way to the HD2. Russian hacker Cotulla, responsible for many of these ports, has just announced the next big port: Windows RT is now running on the HD2.

That's true, but again, it's still not the whole story.
There's an MSO.DLL and an MSORES.DLL that collectively take up 210 MB of RAM.

It's nice to focus on DLLs, but I also said "and a host of other resources". What I mean specifically under that heading is, for instance, garbage collector cruft, i.e. uncollected objects. Even a small GC program can easily accumulate hundreds of megabytes of RSS before the garbage collectors bothers doing something about it.

But these are loaded once -- even if you load all the Office programs simultaneously.

I know, that's why I was talking about shared libraries.

And even then, it doesn't actually take up 210 MB of physical memory. Remember that Windows NT has a demand-paged virtual memory system. Those files are demand-paged into memory, 4 KB at a time. Until one of the Office programs actually calls a function located on a certain page, then that page is not actually taking up any RAM.

I'm fairly certain they are paged at larger increments than that, otherwise the initial execution would be so exceedingly slow that even startup would take minutes to complete. What most likely happens (and I'm simply talking from *nix kernel experience, so feel free to correct me) is that the I/O subsystem pulls the files in in much larger chunks into the I/O buffer cache. Subsequent mapping of pages happens much faster (via process page table manipulation), but the blocks holding the DLL contents still take up space in the page cache, although much less than pulling it in completely in one go and also in an evictable manner subject to other kinds of memory pressure.

The Excel icon now takes 173 KB of disk space. One icon. (At 256x256, 32-bit color, as a high-quality PNG.) Now think about how many other icons there are in Office.

And that is a positive point how exactly? Also, most UI icons, I would hope, are not 256x256x32bpp.

Fonts.

A good-sized compressed TTF font is a few MB in size, at most. Unless there is a couple thousand fonts hidden in office somewhere, this contributes a few dozen MBs at most.

The new equation editor.

Depends. If it's a GUI with controls and some live code behind it, I would give it 10MB of extra. Given some icons and help pages, perhaps 30-40MB.

More accurate statistics functions (the old ones are still there, to get bug-for-bug backward compatibility).

I'm sorry, but now you're into the silly things. This is just a bunch of interpreted code. Perhaps, and now I'm being very generous here, 10MB of new code, 30MB tops. I mean it's not like they re-implemented the entire office suite in it, they just added some utility functions.

So in summary, you're still only 1/10th the way. I know where the 9/10ths went - it's the animated sequences, the uncompressed BMPs on disk, the tons of various pre-made media, like music and video stuff for shit business presentations that nobody likes anyway. If you took it away, I doubt anybody would really complain, but then you wouldn't have the latest and greatest incremental update to sell to your locked-in business customers. There's money to be made!